Motor-control system



Dec. 1 1924- 1,519,257

R. E. HELLMUND MOTOR CONTROL -SYSTEM Filed Jan. 8, L920 INVENTCR Rudolf E. h'el/mund AYTTORNEY wlmzsscs Patented fies. lid, F3324.

UNITED STATES PATENT GFFltiE.

EJ131011 E. HELLMUND 01E SWISSVALE, PENNSYLVANIA, ASSIGNOR TO WESTING- HGTLQE ELECTRIC & MANUFAGTURING COMPANY, A GURPORATION F PENNSYL- VMIILA.

IZEOTGR-CQNTROL SYSTEM.

Application filed January 8, 1920. Serial in). 350,203.

7 '0 all whom it may concern: I

Be it known that I, RUDoLF E. HELL- MUND, a citizen of the German Empire, and a resident of Swissvale, in the county of Al- 55 legheny and State of Pennsylvania, have invented a new and useful Improvement in Motor-Control Systems, of which the follow ing is a specification.

My invention relates to motor-control systerns and particularly to systems for controlling the operation of induction motors of relatively large capacity.

The object of my invention is to provide a system of control for induction motors which shall interposc a definite time interval between the interruption of the starting connections and the establishment of operating connections for motors of the above type.

Auto starters for use with systems of the above designated class have heretofore been dcsigncd to complete the operating connections for the induction motor in the sh0rtest possible time consistent with proper mechanical operation after the interruption of 2 the starting connections.

Experience has taught that, in controlsysten'is that are employed to govern the op eration of induction motors of relatively large capacity, the closure of the operating connections immediately after the starting connections are interrupted, results in an abnormal current wave traversing the motor at the moment connections are so established and causes very unfavorable torque conditions to prevail. These conditions are, in general, much more harmful than the correspending conditions at starting. It has been found that, if a suiiicient time interval for the dissipation of the energy stored in the rotor of the motor is interposed between the interruption of the starting connections and the establishment of the running con neotions, the above unfavorable conditions are avoided. A. detailed discussion of these conditions may be found in Vol. XXXVI of the A. .l. proceedings, p. 321, in an article by myself entitled Transient conditions in asynchrmious machines and their relation to control problems Fig. l of the accompanying drawing is a diagrammatic view of a control system embodying electrical means for accomplishing the object of my invention. Fig. 2 is a View, partially diagrammatic and partially schematic, of a controlsystem employing an auto starter that is provided with mechanical means for introducing an interval. of time between the interruption and reestablishment of the motor circuit in systems of the above character. Fig. 3 is a sectional side view, shown diagrammatically, of the auto starter employed in the system shown in Fig. 2. v i

Fig. l of the drawings illustrates a motor 1 that is adapted to be connected to a supply circuit 2 by means of a starting switch 3 and an operating switch 4. The induction motor 1, which may be ofnny particular type, is provided with an armature 5 and a stator winding 6. A transformer 7,01 other voltage-reducing device, isinterposed between the supply circuit 2 and the stator winding ti of the induction motor when the starting switch 3 is closed. An electromagnctcoil 8 is energized when the control switch 9 is closed in its left-hand or starting position. The switch 3 is also provided with an interlock 10 that is closed when the switch is-open for a purpose hereinafter set forth.

The switch 4 is provided with an actuating coil 11 which is energized from the main supply circuit when the control switch 9is closed in its right-hand or running position. The switch t is provided with an interlock 12 that is adapted to complete a holding circuit for the coil 11 when the switch 4 is closed.

A relay-13, which is adapted, when closed, to partially complete a circuit for coil 11, has an actuating coil 14s that is energized in accordance with the clcctromotive force of the motor winding 6. The relay 13 is so desigifcd that. it is closed only when a voltage of predctern'iincd minimum value is impressed on the coil 14. A line switch 15 is provided to connect the control system to the supply circuit 2.

If it is assumed that the apparatus occupics the positions shown in Fig. 1, the motor 1 is startcd'by closing the line switch 15 and actuating the control switch 9 to its lefthand position. The closure of switch 9 establishes an energizing circuit for the actuating coil 8. The starting switch 3 closes to connect the stator winding 6 of the induction motor 1 to intermediate points of the transformer winding 7 and thereby effects through the interlock 10. Since the coil l-i-l of relay 13 energized in accordance with the voltage of the stator winding 6, the relay 13 will be maintained open until the energy stored in the rotor of the motor is sub stantially dissipated or, in other words, un-

the voltage, of the phase across which the actuating coil 14 of the relay 13 is connec ed decreases to a predetermined minimum value.-

When the relay 13 closes, a circuit es tablished from one side of the supply cir cuit 2, through the interlock 10, relay 13, actuating coil 11 of switch 4 and the control switch 9, to the other side of one phase of the supply circuit. The energization of coil '11 actuatcs switch 4 to its closed position and establishes a holdin circuit for coil 11 by the closure of interlock 12.

In order to. arrest the operation of the motor 1, the control switch 9 is moved to the intermediate position shown in the drawing'to interrupt the circuit of coil 11 and causes switch 4 to open.

For the above system of connections the relay 13 insures that the switch 4 is open so long as the voltage of the stator winding 6 exceeds a predetermined value. In this manner, the motor 1 is protected from abnormal current and, torque conditions that would. prevail in such motors if the switch. 4 were closed immediately upon the closure of switch 9. This interposed period of time is not of sufficient duration to cause a material decrease in the speed ofoperation of the motor. 1

. T he system shown in Fig. 2 of the accompanying drawing comprises an induction motor 1 that is connected t the supply circuit 2 by means of an auto-starter 16 and the line switch 15. The auto-starter which is shown diagrammatically in Fig. 3 of the drawing, comprises an operating handle 18 and sets of contactors 20 and 21.

with apertures 28 and 29. The set of contactors 21 has stationary contact members iii) and movable contact members 31 which co-operate with the stationary contact members and-are mounted on an insulating rod A bracket 33, having an aperture 34, provided to operate the set of contactors The operating handle 18 is pivotally. mounted in a bracket 35 and is provided with an arm 36 that is adapted to enter aperture 28 or aperture 34, depending uponthe direction in which the handle is moved, to actuate the corresponding set of contactors. The arm 36 is so designed that its upper surface engages the bracket-andexerts a cam action thereupon which tends to separate the corresponding contactors. Thus, when the arm'36 engages bracket 27, contactors' 20 are separated and, when the arm 36 en agcs brackets 33, contactors 21 are opens and the remaining contactors are free to close.

A. dash-pot device 37 is adapted to maintain contactor set 20 open after the arm 36 releams bracket 27. The dash-pot device 37 is provided with n plunger 38 which engages aperture 29 of bracket 27 to maintain contactor 20 open when the operating handle 18 initially releases the movable contactors 23. The opposite end 39 of the lunger engages the handle 18 to force t e plunger into the aperture 29 when the handle 18 is moved to the position shown in Fig. 3. At one end, a spring 40 is connected to the plunger 39 and at the other end, to the handle 18 in such manner that, when the handle is moved to actuate contactors 21, the spring tends to withdraw plunger 38 from aperture 29. The instantaneous withdrawal of plunger. 39 from aperture 38 is opposed by the action of piston 41- of the dash-pot which delays the release of the bracket 27 an interval of time. depending upon adjustment of the dash-pot.

The remaining apparatus shown in F ig. 2 is similar to that shown in Fig. 1. and, since it performs similar functions, it is similarly designated in the drawing, and further description is deemed unnecessary.

In order to operate the system shown in Figs. 2 and 3, the handle 18 of the auto starter is first moved to the left, as viewed in Fig. 3. Line switch 15 is then closed and a circuit is established from the supply circuit 2, through line switch 15, transformer winding 7 and contactors 21, to the stator winding 6 of the motor. The inter posed transformer winding 7 impresses a reduced voltage on the motor winding 6 and starts the operation of the motor. Contactors 21 are closed by springs 25, and contactors 20 are maintained open by the engagement of arm 36; and bracket 27. The plunger 38 is forced through aperture 29 of the bracket. j

From this position,

the handle 18 of the auto starter is moved to the right-hand posi-.

tion. The arm 36 enga es a erture 34 of the bracket 33 and thereby li ts the contactors 21 to interrupt the circuit to the motor winding 6. When the arm 18 is moved to the right, the spring 40 is placed under ten sion and it tends to withdraw the plunger 38 from the bracket 27 to permit contactors 20 to close. The piston 41 opposes the withdrawal of plunger 38. The period of time that is required for the operation of the dash-pot 37 to disengage plunger 38 from the bracket 27 in order that contaotors 20 may close, determines the interval of time that is interposed between the interruption of the starting circuit that is established by contactors 21 and the re-establishment of the operatinggcirouit by the closure of contactors 20. y suitable adjustment of the dash-pot 37, an interval of time may be interposed between the starting connections for the motor and the operating connections of the motor that is of sufficient extent to insure the dissipation of the energy stored in the rotor of the motor stator without permitting a material decrease in the motor speed, and, therefore, to protect the motor 1 from an abnormal rush of current and from-- abnormal torque conditions that would otherwise prevail. The operation of the system described in Fig. 2 may be arrested by openin the line switch 15.

Althougli I have described only simple and preferred forms of my invention, the invention is not so limited and I desire, therefore, that only such limitations shall be imposed as are indicated by the spirit and scope of the appended claims.

I claim as my invention:

1. In an auto starter, the combination with a plurality of contactors biased to a closed position, of an operating handle adapted to open certain of said contactors, and a dash-pot device adapted to maintain said contactors open a predetermined time after said handle has been moved to open certain other of said contactors.

Kan-

2. In an auto starter, the combination with a plurality of contactors biased to their closed positions, and an operatin handle having two positions, said hande being adapted, when in one position, to open a up of said contactors and adapted, when m a second position, to open a second group of said contactors and permit said first group of contactors to close, of a dash-pot adapted to maintain said first oup of contactors open fora predetermined interval after said handle is moved to the second position to open said second group of contactors.

3. A switching device comprising a contactor biased to its closed position and having an apertured supporting arm, and an operating handle having an arm normally free of said aperture and adapted to enter the aperture of said supporting arm to open said contactor.

4. A switching device comprising a contactor biased to its closed position and having an apertured supporting arm, an operating handle having an arm adapted to enter the aperture of said supporting arm to open said contactor, and a dash-pot having a member adapted to maintain said contactor open a predetermined interval of time after said handle has been moved to release said contactor.

5. A switching device comprising a contactor biased'to its closed position and having an apertured supporting arm, an operating handle having an arm adapted to enter the aperture of said supportingarm to open said contactor, a dash-pot having a member adapted to maintain said contactor open a predetermined interval of time after said handle has been moved to release said contactor, and a second contactor adapted to be opened when said arm occupies said lastnamed position.

In testimony whereof, I have hereunto subscribed my name this 8th day of Decema ber, 1919.

' RUDOLF E. HELLMUND. 

